Process of producing technical grade



United States Patent PROCESS OF PRODUCING TECHNICAL GRADE QUINOLINE Hans Wille and Rudolf Oberkobusch, Duisburg-Meiderich, Germany, assignors to Gesellschaft fuer Teerverwertung m.b.H., Duisburg-Meiderich, Germany, a corporation of Germany No Drawing. Application July 18, 1956 Serial No. 598,497

Claims priority, application Germany July '18, 1955 7 Claims. (Cl. 260-283) The present invention relates to a process of producing quinoline and more particularly to a process of producing quinoline from a mixture containing quinoline and other bases, especially bases the boiling po'nts of which are like that of quinoline or are near its boiling point and especially from coal tar bases containing quinoline.

As is well known, the recovery of quinoline from such mixtures encounters considerable difficulties.

According to such known processes quinoline bases are extracted, for instance, from coal tar or similar starting materials containing heterocyclic and aromatic bases by means of dilute acids, for instance, by means of 30% sulfuric acid. Such starting materials are coal tar fractions previously freed of phenols and boiling within a temperature range between 200 C. and 260 C. and especially coal tar fractions which have a boiling point near that of quinoline, i.e. around 238 C.

In this known extraction process there are extracted, in addition to quinoline, varying amounts of other bases depending upon the boiling range of the starting fraction employed. Such other bases are, for instance, methyl or ethyl homologues of pyridine, aniline, quinoline, isoquinoline, and isoquinoline itself as well as bases of unknown constitution. All these other bases are present in the resulting so-called crude quinoline which is obtained by separating the hydrocarbon layer from the acid aqueous containing the acid addition salts of said bases and precipitating the bases therefrom by the addition of alkaline precipitating agents.

Technical grade quinoline is obtained by fractional distillation of said crude quinoline. The goal to be achieved thereby is substantially complete separation of quinoline from its accompanying bases. However, such a separation can be accomplished only to a certain extent by using rectification columns provided, for instance, with 15 to 25 theoretical trays. Thereby, technical grade quinoline of 85% to 90% purity is obtained.

However, production of a technical grade quinoline of a degree of purity of 95% and more requires expenditures, i.e. columns with a large number of theoretical trays and a reflux ratio, which are entirely disproportionate to the desired result. This is due to the presence of bases which have a boiling point like that or similar to that of quinoline.

Technical grade quinoline of a degree of purity of 95% and more can also be produced by making use of the differences in basic'ity of the compounds present in crude quinoline. However, such a procedure also requires very considerable expenditures because distribution columns of especially high efficacy are required. Such distribution columns are just as uneconomical for the large scale production of quinoline as the highly effective rectification columns required for separating by distillation the above mentioned accompanying bases.

Purification processes by means of the sulfate or phthalate also require considerable expenditures. 'It is evident that, heretofore, none of the known processes has solved the problem of recovering technical grade quinoline from such mixtures "in a fully satisfactory manner. v

It is one object of the present invention to provide a simple and effective process of producing technical grade quinoline of a degree of purity of and more from mixtures of quinoline with accompanying bases of the same or a similar boiling point which process does not require disproportionately high expenditures and complicated apparatus. I

Other objects of the present invention and advantageous features thereof will become apparent as the description proceeds. I

In principle, the process according to the present invention consists in treating the starting material, i.e. the mixture of quinoline and accompanying bases, especially bases that have a boiling point substantially corresponding to that of quinoline, with aqueous formaldehyde solution at elevated temperature at atmospheric or superatmospheric pressure for several hours. The preferred procedure comprises heating under reflux the quinoline containing starting mixture with aqueous formaldehyde solution. Especially advantageous has proved the addition of an acid catalyst such as oxalic acid, during formaldehyde condensation.

The amount of formaldehyde added must at least be sufiicient to supply one mol of formaldehyde for each mol of accompanying base. Preferably an excess of formaldehyde is used, for instance, an excess of 10% to over said amount.

When proceeding in this manner, the bases accompanying the quinoline are completely condensed with said formaldehyde inasmuch as they are substituted primary bases. They are condensed therewith to a rather substantial extent inasmuch as they are pyridine or quinoline bases having alkyl groups in their pyridine or quinoline nucleus. Thereby, resins of a very high boiling point are formed. Condensation is readily effected in such a manner that the non-reacted bases can comparatively easily be rectified in conventional distillation columns with about 20 to 30 theoretical trays and a reflux ratio, of, for instance, 10-15z1, to yield quinoline of at least 98% purity or even commercial, pure quinoline. In this process it is advisable to remove odoriferous, partly condensed constituents of the formaldehyde-treated base mixture by washing with water, if necessary, repeatedly.

In general, the starting material, for instance, base mixtures derived from coal tar, contains about 50% of constituents which can be separated with 'difliculty only or not at all, and which consists of more highly substituted primary bases. The starting mixtures often contain also small amounts of residual .phenols which frequently are present during vacuum distillation as amphoteric addition compounds with said bases. Such addition compounds can be removed only with difiiculty since they are rather stable on boiling.

When treating the starting material with formaldehyde at elevated temperature according to the present invention, the accompanying bases of the same or a similar boiling point as that of quinoline are condensed with said formaldehyde and, thus, are removed. Their removal facilitates subsequent separation of the remaining mixture by fractional distillation and considerably increases the yield and improves the quality of the resulting quinoline.

After the treatment with formaldehyde according to the present invention followed by washing with water, the remaining base mixture consists mainly of isoquinoline and quinoline which are separated by fractional distillation. It is comparatively easy to effect such a separation by distillation because isoquinoline has a boiling point which is about .3 C. higher than that of quinoline. The process according to the present invention, thus, also permits the production of isoquinoline in a better yield and of a greater degree of purity than heretofore possible.

All bases having a lower boiling point than quinoline are removed by the process according to the present invention.

Thus, preliminary treatment of the mixture of bases with formaldehyde at elevated temperature reduces the problem of separating by fractional distillation a multicomponent mixture which, heretofore, has not been solved satisfactorily, to the comparatively simple problem of separating by fractional distillation a two-component mixture. Hence, the process according to the present invention permits to produce technical grade quinoline of a degree of purity of 95% and more as well as isoquinoline of a comparatively high degree of purity in a very economical manner. 'In addition thereto, resinous products are obtained which can be used as thermoplastic binding agents.

According to another embodiment of the present invention, condensation with formaldehyde is effected in the presence of added phenolic compounds, for instance, of phenol itself, or of cresols or of higher phenols. Such a procedure results in a substantially complete separation of all primary bases present in the starting material so that 'a purified quinoline containing less than 0.2% of primary bases (within the limit of error encountered in titrimetric analysis) is obtained. By way of comparison it may be pointed out that technical grade quinoline obtained under the same conditions of fractional distilla tion but without preliminary treatment with formaldehyde has a content of primary bases between 2% and 5% whereby, furthermore, the yield is considerably lower.

According to the present invention not only the primary bases are separated but also the above mentioned residual phenols which, as such, have a lower boiling point but which form molecular compounds with a boiling point similar to that of quinoline. Such residual phenols are also condensed with formaldehyde to resins remaining in the residue so that heretofore used preliminary purification steps for the removal of said phenols can be omitted.

In addition to the above described advantages, the process according to the present invention has the further advantage that the resulting quinoline does not tend to become discolored under the influence of air and light or'that discoloration of said quinoline does not take place as rapidly as with quinoline produced in the heretofore employed manner. Quinoline obtained or, respectively, purified according to the present invention can be used for all those purposes where a light color is of importance.

The following example serves to illustrate a preferred embodiment of the present invention without, however, being limited thereto and to compare said process with the heretofore known process.

Example 20 metric tons of crude quinoline of the solidification point of 32.4 C., boiling to about 95 within a boiling range of, for instance, about 4 C., are heated to boiling under reflux with 3 metric tons of 30% aqueous formaldehyde solution and 100 kg. of technical grade oxalic acid for four hours. The apparatus used for the condensation is a still provided with agitating device, reflux condenser, heating arrangements and a distillation column attached thereto. After condensation is complete, the aqueous layer is drawn off. The treated quinoline is thoroughly washed with 4 cu. m. of water while stirring. Such washing is repeated once. The wash waters are drawn off. The remaining washed crude quinoline is rectified by means of a column having 22 theoretical trays at a reflux ratio of 15:1. As soon as 2.5% of the quinoline charge have distilled over, the distillate has a solidification point of -17.5 C. On further distillation the distillate attains the optimum solidification point of l5.7 C., i.e. it is of the quality of commercial, pure quinoline.

13 metric tons corresponding to 65% of the initial charge are recovered in the form of technical grade quinoline of the average solidification point of 16.2 C. Such a quinoline has a degree of purity of 98% is free of primary bases, and remains light-colored on storage for a considerable period of time.

Without formaldehyde treatment according to the present invention, the same crude quinoline is distilled under the same conditions of rectification in the same column. It yields only 9 metric tons, i.e. 45.5% of quinoline of a solidification point of 18.8 C., i.e. corresponding to a degree of purity of just about Its content of primary bases is determined by titration to 2.8%. The resulting quinoline has a considerably greater tendency to rapidly become darkly colored than quinoline purified by means of formaldehyde according to the present invention.

As stated above, condensation with formaldehyde may be carried out under pressure, i.e. on heating the mixture of bases and, if desired, additional phenol with formaldehyde in an autoclave to a temperature between about 100 C. and about 150 C. and preferably to a temperature of C. In general, a pressure above 6 atmospheres should not be exceeded. Otherwise, the reaction proceeds as described in the example. Operation under pressure accelerates the condensation reaction of formaldehyde with the accompanying substituted bases.

The preferred temperature during condensation of the accompanying substituted bases with formaldehyde is the temperature of boiling under reflux. However, condensation may also be effected at a lower temperature or, when operating under pressure as stated hereinabove, at a higher temperature. The temperature should not be lower than 100 C.

The preferred aqueous formaldehyde solution employed in the condensation step is a 30% formaldehyde solution. However, formaldehyde solutions between 30% and 40% may also be used.

Oxalic acid is the preferred acid catalyst. However, other acid catalysts as they are conventionally used in acid condensation of phenol and formaldehyde can be employed, such as acetic acid, HCOOl-I, HCl (diluted), H 80 (diluted), but also phenols.

Additional phenols can be added in an amount up to 5% calculated for the crude quinoline employed as starting material. It is understood that corresponding additional amounts of formaldehyde must be added to the mixture.

To recover isoquinoline from the formaldehyde-treated crude quinoline, distillation is continued up to a boiling point of 245 C. The resulting fraction represents isoquinoline with a melting point of l0 C. and a degree of purity of about 30%. It is obtained in an amount of metric tons corresponding'to 6% of the initial charge.

Of course, many changes and variations in the starting material employed, the concentration of the formaldehyde solution used, the condensation conditions, temperature, pressure, and duration, the distillation columns used and the reflux ratio employed, and the like may be made by those skilled in the art in accordance with the principles set forth herein and in the claims annexed hereto.

We claim:

1. In a process of producing technical grade quinoline of a degree of purity of at least 95 the steps comprising heating a fraction of coal tar bases containing quinoline and coal tar bases of approximately the boiling point of quinoline, said fraction boiling within a boiling range of about 4 C. at about the boiling point of quinoline, with formaldehyde at a temperature between about 100 C. and about C. to cause resinification of the alkyl substituted bases of said fraction, and subjecting the reaction mixture to fractional distillation to distill oil the non-resinified bases from the resinified reaction product and to fractionate the distilled non-resinified bases into a technical grade quinoline fraction of a degree of purity of at least 95% and an isoquinoline fraction.

2. In a process of producing technical grade quinoline of a degree of purity of at least 95%, the steps comprising heating a fraction of coal tar bases containing quinoline and coal tar bases of approximately the boiling point of quinoline, said fraction boiling within a boiling range of about 4 C. at about the boiling point of quinoline, with formaldehyde at a temperature between about 100 C. and about 150 C. and with the addition of an acid condensation catalyst to cause resinification of the alkyl substituted bases of said fraction, and subjecting the reaction mixture to fractional distillation to distill off the non-resinified bases from the resinified reaction product and to fractionate the distilled non-resinified bases into a technical grade quinoline fraction of a degree of purity of at least 95% and an isoquinoline fraction.

3. The process according to claim 2 wherein the acid catalyst is oxalic acid.

4. In a process of producing technical grade quinoline of a degree of purity of at least 95 the steps comprising boiling under reflux a fraction of coal tar bases containing quinoline and coal tar bases of approximately the boiling point of quinoline, said fraction boiling within a boiling range of about 4 C. at about the boiling point of quinoline, with an aqueous formaldehyde solution to cause resinification of the alkyl substituted bases of said fraction, separating the aqueous layer, repeatedly washing the reaction mixture with Water, and subjecting the reaction mixture to fractional distillation to distill off the nonresinified bases from the resinified reaction product and to fractionate the distilled non-resinified bases into a technical grade quinoline fraction of a degree of purity of at least 95% and an isoquinoline fraction.

5. In a process of producing technical grade quinoline of a degree of purity of at least 95 the steps comprising boiling under reflux a fraction of coal tar bases containing quinoline and coal tar bases of approximately the boiling point of quinoline, said fraction boiling within a boiling range of about 4 C. at about the boiling point of quinoline, with an aqueous formaldehyde solution with the addition of an acid condensation catalyst to cause resinification of the alkyl substituted bases of said fraction, separating the aqueous layer, repeatedly washing the reaction mixture with water, and subjecting the reaction mixture to fractional distillation to distill ofi the nonresinified bases from the resinified reaction product and to fractionate the distilled non-resinified bases into a technical grade quinoline fraction of a degree of purity of at least and an isoquinoline fraction.

6. The process according to claim 5, wherein the acid catalyst is oxalic acid.

7. In a process of producing technical grade quinoline of a degree of purity of at least 95 the steps comprising boiling under reflux a fraction of coal tar bases containing quinoline and coal tar bases of approximately the boiling point of quinoline, said fraction boiling within a boiling range of about 4 C. at about the boiling point of quinoline, with an aqueous formaldehyde solution with the addition of an acid condensation catalyst to cause resinification 0f the alkyl substituted bases of said fraction, separating the aqueous layer, repeatedly washing the reaction mixture with water, subjecting the reaction mixture to fractional distillation to distill off the non-resinified bases from the resinified reaction product and to fractionate the distilled non-resinified bases into a technical grade quinoline fraction of a degree of purity of at least 95% and an isoquinoline fraction, and collecting the quinoline fraction having a degree of purity of at least 98%.

References Cited in the file of this patent UNITED STATES PATENTS Stewart Nov. 12, 1946 OTHER REFERENCES 

1. IN A PROCESS OF PRODUCING TECHNICAL GRADE QUINOLINE OF A DEGREE OF PURITY OF AT LEAST 95%, THE STEPS COMPRISING HEATING A FRACTION OF COAL TAR BASES CONTAINING QUINOLINE AND COAL TAR BASES OF APPROXIMATELY THE BOILING POINT OF QUINOLINE, SAID FRACTION BOILING WITHIN A BOILING RANGE OF ABOUT 4* C. AT ABOUT THE BOILING POINT OF QUINOLINE, WITH FORMALDHYDE AT A TEMPERATURE BETWEEN ABOUT 100* C. AND ABOUT 150* C. TO CAUSE RESINIFICATION OF THE ALKYL SUBSTITUTED BASES OF SAID FRACTION, AND SUBJECTING THE REACTION MIXTURE TO FRACTIONAL DISTILLATION TO DISTILL OFF THE NON-RESINIFIED BASES FROM THE RESINIFIED REACTION PRODUCT AND TO FRACTIONATE THE DISTILLED NON-RESINIFIED BASES INTO A TECHNICAL GRADE QUINOLINE FRACTION OF A DEGREE OF PURITY OF AT LEAST 95% AND AN ISOQUINOLINE FRACTION. 